Deep vein thrombosis (DVT) is characterised by the development of a clot within a deep vein anywhere in the body but almost exclusively in the veins of the calf or thigh. DVTs are a large source of morbidity, the most common serious complication of DVT being a pulmonary embolism whereby a blood clot breaks free from a vein wall, travels to a lung and blocks an artery.
The following factors can promote blood clot formation within a vein:                1. Increased coagulation of the blood (e.g. women on hormones);        2. Increased clotting factors in the blood;        3. Damage to a vein wall (e.g. trauma to a leg), whereby coagulation factors are released and a chemical cascade causes a clot to form; and        4. Stasis of the blood, as happens in dependant limbs where gravity causes decreased blood flow through the veins. Blood clots are known to form most frequently in the legs due to stasis.        
The circulatory system circulates blood around the body using various mechanisms. The heart pumps blood into the arterial system and this system distributes blood to every part of the body. Above the heart, gravity plays a role in returning blood to the heart, and below the heart, muscular contractions compress veins to move the blood towards the heart. Directional valves of the veins ensure that blood flow is directional. Small muscle groups move small amounts of blood during each contraction of the leg muscle and this is important as, since vein walls are thin and elastic, too much blood in a vein could cause the vein to distend, to suffer damage and to render the directional valves non-functional.
During long periods of muscular inactivity (e.g. when travelling on an aeroplane, car, bus or train, when confined to a wheelchair, or when bed ridden), the risk of a blood clot forming in a person increases as there may be little or no venous blood movement within the legs of the person. In addition to stasis, with blood continuing to collect within the leg veins, the directional valves may leak, the veins may distend and suffer damage and hence release clotting factors which could also initiate clot formation.
Compression sleeves for preventing DVT are known. However, although such sleeves may decrease the risk of a blood clot forming, the sleeves generally have the disadvantage that they do not decrease the risk to an acceptable level. In particular, those sleeves that compress a large area of muscle at any given time and consequently squeeze large volumes of blood through the veins may have the following disadvantages:
1. During compression of the sleeve, blood may be squeezed back into veins below the sleeve, thus increasing stasis in, and causing further distension of, the veins below the sleeve. This problem is exacerbated by long sleeve compression times, large compressed areas and if the veins located beneath the sleeve already contain too much blood.
2. Following compression, the sleeve is relaxed, and as the empty veins in the previously compressed muscle refill with blood from below the sleeve, there is no blood to push along the blood in the veins above the sleeve and thus the blood in the veins above the sleeve lies static until the sleeve is next compressed.
3. If there is any constriction of the veins above the sleeve, such as the veins located in a seated person's thighs, then the large volume of blood may distend and damage those veins.
To recapitulate, some of the known compression sleeves have disadvantages in that they can aggravate stasis below the sleeve during compression of the muscle, they cause stasis above the sleeve when the sleeve is relaxed, and may distend vein walls and render directional valves of the veins non-functional, thus increasing the risk of blood clot formation. This is also true of those sleeves that have a series of inflatable chambers and which compress areas of a leg sequentially, as the chambers, which envelop a large area of muscle, do not deflate until all of the chambers have inflated.
Post-surgical patients, particularly patients who have undergone orthopaedic surgery, are at the greatest risk of developing DVT in the six week period following surgery. Typically orthopaedic surgical out-patients spend only a period of 24 hours or up to 5 days in hospital under supervised care despite the long period of time during which the risk of DVT is elevated. During the post-surgical period in hospital, patients are as a matter of course provided compression stockings and may be treated with usually large, cumbersome compression machines which employ compression sleeves which either cover the entire limb of the patient or act to compress a large region of the patient's body or limb. The inventors have recognised that the use of compression upon a large portion of the patient's limb is to a great extent redundant as the same or better prophylaxis can be achieved by focusing compression upon a small and well defined portion of the limb.
The use of large, cumbersome compression machines in hospitals requires the immobilisation of the patient. Typically, the compression machines and sleeves are designed to operate only whilst the patient is in bed and attached to the compression machine and such machines and sleeves are large, cumbersome devices that do not permit patient ambulation. This leads to a decrease in patient compliance whilst in hospital, as they are required to remove the compression sleeves to move around and during the post-hospital admittance period during which time they will not be subjected to compression prophylaxis due to the unavailability of compression machines (which are large, cumbersome and costly) during the period of greatest risk of DVT whilst the patient recovers at home.
Similarly, known compression devices are not configured in such a manner that they are adaptable to use on transportation conveyances such as airplanes, trains, and other motor vehicles. This increases the risk of developing a DVT amongst susceptible populations.
Compression machines and sleeves currently in use also suffer from the disadvantage of uneconomical design and configuration in so far as they incorporate compression means which are unwieldy, unnecessarily complicated, not aesthetically pleasing and require the use of multiple tubes connected to a pump for inflating the compressors of the compression sleeve or sleeves. This makes apparatus currently known and in use cumbersome.